Method and apparatus for etching



March 4, 1958 c. SKLADAL, JR 1 METHOD AND APPARATUS FOR ETQHING I 3Sheets-Sheet 2 Filed Sept. 3, 1953 ATTOk/VEYJ Fig.7

Mrcl 4, 1958 c. SKLADAL, JR 2,825,167

METHOD AND APPARATUS FOR ETCHING Filed Sept. 3, 1953 3 Sheets-Sheet 3METHOD AND APPARATUS FOR ETCHING Conrad Skladal, JL, Dallas, Tex.,assignor to Texas Instruments Incorporated, Dallas, Tex., a corporationof Delaware Application September 3, 1953, Serial No. 378,337

16 Claims. (Cl. 41-9) This invention relates to a method and apparatusfor etching and more particularly, to an etching process as a result ofwhich electrical circuits are printed, the printing being by thedissolution of portions of an electrically conductive sheet through theagency of a fluid capable of etching and apparatus for carrying outsame.

An accepted standard technique for producing printed circuits originateswith the step of bonding a sheet of copper of approximately .001 to .003inch in thickness to a corrosion resistant plastic base. The copper,required to form the electrical circuit, is then covered by an enamelthat is resistant to the fluid employed for the etching. When a printedcircuit is thus prepared and is treated with a fluid capable of etchingcopper, the copper not coated with the enamel dissolves and the desiredcircuit is thereby produced. A fluid commonly used to etch copper isferric chloride. With the proper process conditions copper is readilysoluble in this fluid. Since the plastic base and the enamel arecorrosion resistant, the coated copper is unaffected by the process andthe desired circuit remains bonded to the plastic base.

As the printed circuit process above described depends upon thedissolution of copper in a ferric chloride solution, the equipment usedmust be corrosion resistant to ferric chloride to operate satisfactorilyfor any length of time. In one successful and satisfactory type ofapparatus, a stone tub is used as the etching fluid container. A shaftextends through one wall of the tub and is driven by a motor locatedoutside of the tube. A series of cupshaped paddle wheels are mounted onthe end of the shaft'inside the tub and are either formed from rubber orcovered with rubber. The portion of the drive shaft inside of the tub isalso rubber covered. The circuit to be etched is suspended above thepaddle wheels in a suitable location and as the shaft is turned by themotor, the etching fluid is thrown against the printed circuit and thecopper unprotected by the enamel is dissolved. As stated, this apparatusproduces very satisfactory printed circuits in a short time, but theinitial cost of the equipment is high.

In another type of apparatus a glass tub is utilized as the container.Mechanical agitation of the etching fluid is provided by either amechanical rocker system located externally of the tub or by amechanical stirrer extending down into the fluid Satisfactory plates areproduced by this type of apparatus, but the time required to print eachcircuit varies from 60 to 80 minutes. In place of using the mechanicalstirrer, a submerged header ring formed with a series of holes andconnected outside of the glass tub to a source of air can be used. Asair is supplied to the header, the etching fluid is agitated by the airfrom the header bubbling through the fluid. This type of apparatus iseven more satisfactory since the time required to produce each plate isreduced to approximately 45 minutes.

Another type of apparatus uses a glass spray gun to aspirate the etchingfluid against the surface of the article to be etched. Air underpressure supplied to the nozzle nitcd States Patent "ice of the spraygun picks up the etching fluid and sprays it against the surface of thecircuit to be printed. Besides producing plates of a high quality, theuse of the spray gun type of equipment further reduces the productiontime for each plate to about 10 to 15 minutes per plate.

It should be noted at this point that when using ferric chloride as theetching fluid, agitation is an essential step in the process due to thechemical reactions involved. The agitation introduces oxygen into thefluid which liberates free chlorine to combine with the copper and formcopper chloride. Copper chloride is a soluble salt in acetic solutionsand since ferric chloride is acetic to a certain extent, the copperchloride dissolves back into the etching fluid. In addition toliberating free chlorine from the solution, agitation also assists inremoving the copper chloride from the surface of the plate as it formsand thus keeps a fresh copper surface exposed to the action of the freechlorine.

According to the present invention a novel apparatus and method arepresented to cut down the production time for each plate appreciablywithout loss of quality. More specifically, this invention utilizes anozzle or nozzles submerged in the etching and connected with a sourceof air. The nozzle or nozzles are provided with a venturi passage sothat a reduction in the supply air pressure is converted into acorresponding increase in velocity. This stream of high velocity air onemerging from the nozzle carries a stream of etching fluid upward tostrike against the surface of the prepared circuit suspended above thelevel of the fluid. It has been found that this stream of air does notproduce turbulence in the fluid but draws the fluid instead from allsides in a streamlined flow to produce a steady stream of high velocityfluid. This streamlined flow appears to form walls which take the placeof the outer jet of the usual ejector pump. Thus, besides acting todissolve the copper surface, the stream of fluid tends to remove thecopper surface by a scrubbing action not possible with the mist producedby the spray gun apparatus. A cover and seal are provided for each formof apparatus of the invention to prevent the loss of fluid and to trapfumes which would otherwise escape and corrode nearby objects.

Accordingly, it is a principal object of this invention to provide amethod and apparatus for etching printed circuits that is simple,inexpensive in construction, and that will produce printed circuits inmuch less time than is possible with comparable equipment.

It is another object of this invention to provide an apparatus in whichthe arrangement can be varied to utilize a number of nozzles to reducethe etching time over that possible when using a single nozzle.

It is another object of this invention to provide a construction inwhich the fumes produced during the process are trapped and removed in amanner to eliminate the tendency to corrode nearby objects as well as tomake working conditions more pleasant.

It is still a further object of this invention to provide an arrangementsuitable for the continuous production of printed circuits.

Other and further objects of the present invention will appear from thefollowing detailed description when taken in conjunction with thedrawings in which:

Figure 1 is a view in vertical section of one form of the inventionshowing apparatus suitable for producing a single printed circuit thatutilizes a single nozzle;

' Figure 2 is a view in section through the nozzle sho ing the venturipassage;

Figure 3 is a view in plan showing an arrangement wherein more than onenozzle is used in the production of printed circuits; 1

Figure 4 is a view in section along line 4-4 of Figure 3;

Figure 5 is an exploded perspective view illustrating 3 anlapparatussuitable'for the continuous production of printed circuits;

Figure 6 is a view in section of the apparatus shown in Figure Figure 7is a view in end elevation partly broken away of the apparatus shown inFigure 5; and

Figure 8.is a view in section showing the support for the plate circuitholders.

Referring now to the drawings, Figure shows an apparatus suitable forproducing a single printed circuit. The etching fluid is placed in acontainer which consists of a bottom it), a cylindrical inner wall 11.,and a cylindrical outer wall 12. The inner wall 11 of the container isconsiderably higher than the outer wall 12 and acts as a support for alid 13. A series of rectangular areas 16 are formed around the uppercircumference of wall 11 to provide spaced air outlets; consequently,lid 13 is actually supported by the portionsof the wall 11 between therectangular openings 16. The fluid container and its asso -ciated wallstructure can be formed from a material corrosion resistant to theetching fluid as for example, glass or any suitable plastic such aspolystyrene or an acrylic esin.

Lit 13 is a comparatively flat circular disc preferably made from aplastic material such as an acrylic resin that canbc machined. Lid 13 isturned down in two successive steps from its original diameter to leavetwo annular areas designated respectively as 26 and 26a. A circularcylinder 15 is supported by lid 13 from the annutar area 25 and in likemanner, a circular cylinder 14 is supported by lid 13 from the annulararea 26a. As shown, cylinder 15 is of considerably greater length thancylinder 14. When lid 13 is in place on the fluid container, inner wall11 is positioned between the'cylinders 14 and 15 and cylinder 15'extends downward and is located bet\ 'ec inner wall 11 and outer wall 12of the fluid container. The circuit to be etched, plate 33, is supportedat the centcr of lid 13 by any suitable type of non-corrosive clips 34and 35. inlet tube 19 to extend outward from the container.

A nozzle plate 17, constructed as shown in Figures 1 and 2, isessentially arectangular plate and drilled with holes 23 and 24 toreceive the air inlet tube 19 and nozzle 18, respectively. In thepreferred construction, air inlet tube 1.9 and nozzle 18 form a forcefitwith holes 23 and 24. As an alternative threaded connectioncan be used.in the center of each hole 23 and 24 is-a smaller diameter hole 23:: and22, respectively, that connects into either end of the main airpassage21. The main air passage 21 for this, nozzle plate construction extendsslightly past the mid-point along the length of the nozzle plate sinceonly a sin gle centrally located nozzle 18 is used.

The structure of the nozzle plate may take'aform similar to that shownin Figures 3 and 4 when it is desired bers in Figures 3 and 4 for thesame parts or'functions as used in Figures 1 and 2., Figure 4 shows airinlet tube 19 placed in a forced fit with a hole 23 drilled into plate32. Hole 23 is connected with main air passage 21 by passage 23a ofreduced diameter. Main air passage .21 extends surficiently across plate32 to allow a plurality of passages 22 to connect the nozzles 18 withpassage 21. A series of enlarged holes 24 are drilled into nozzleplate'32 to receive the bases of nozzles 18. Therows ofparallelnozzleson either. side .of the central .row are provided with-a1r by means of passages 33a drilled at right angles tothe i'nain airpassage 21. I

Regardless of whether a .single nozzle oraplurality of Lid 13 isprovided with a hole 25-to allow air a 'paratus of Figure 1 is the same.

nozzles is used, the assembly and function of the ap- The nozzle plateis placed into the bottom of the fluid container with the air inlet tube19 extending upward. The etching fluid is then placed in the containerto some appropriate level such as indicated by the dotted line 27 butsuflicient to submerge the nozzle or nozzles. Since there is noconnecting passage between the areas enclosed by the circular inner wall11 and that enclosed by the outer wall 12, the area between the walls 11and 12 must be filled separately. This area can be filled with eitherthe etching fluid or some other fluid such as water and to a levelindicated by the dotted line 28. if the two areas should beinterconnected, it is clear that both the inner and outer areas definedby walls 11 and 12 will be filled with the etching fluid. Lid 13 withthe cylindrical skirts 14 and 15 is placed in position on the fluidcontainer with the air inlet tube 19 extending through hole 25. Flexibletube 20 then fits over air inlet tube 19 and is connected to a source ofcompressed air.

As air is supplied to the nozzleor nozzles through tube 1.9 and passages23a, 21 and 22, the high velocity air stream carries the etching fluidupward in a streamlined flow to impinge against and etch plate 33. Afterstriking against the plate, a large percentage of the etching fluidreturns to the main body of the fluid, but a portion remains suspendedin the air as fine particles. It is to be noted that cylinder 14extends'downward very close to but does notquite contact the surface ofthe fluid. Therefore, an air outlet passage 29 is provided which forcesthe air to travel in a path downward and through the area 29, upwardbetween walls 11 and 14, out through the opening s16 and downwardbetween walls 11 and 15. A portion of the fluid settles out of the airas it travels downward and through the area 29 and the remaining portionofthe fluid is separated from the air by the fluid trap provided by theliquid between the Walls 11 and 12 before reaching the atmosphere. Thus,the air baffle and seal combine to separate the etching fluid from theair and eliminate the noxious and corrosive fumes that would otherwisebe present due to the etching process.

An apparatus similar to that of Figure 1 in principle, but adapted forcontinuous production of printed circuits is shown in Figures 5, 6 and7. The apparatus consists of two principal assemblies as illustrated inthe exploded perspective'view of Figure 5. Discussing first the lowerassembly "of Figure 5, the fluid container is designated generally bythenumeral 40 and is essentially a hollow rectangular box with a flatraised central portion 41 and a substantially deeper portion 42 and 43at either end. The purpose of this type of arrangement will be discussedin a subsequent paragraph. The container can be'formed ofstainlesssteel, glass, rubber, or a polystyrene plastic. The plastic is thepreferred material since it can be molded, cemented, or fastenedtogether by means such as screws. The nozzle plate 44 is mounted on theraised centralportion 41 of the container and mounts a plurality ofnozzles '18. Air inlet tube 19 connects into the main air passage 21drilled in nozzle plate '44 and forms a fluid tight connection with hole45 in the raised portion 41 of contanier'40. The nozzles 18 fit intoenlarged holes 24 drilled into nozzle plate 44 and are connected bypassages 22 with the main air passage 21. It will be appreciated thatthere are several rows of nozzles 18 suitably connected with the mainair passage 21.

The assembly designated generallyby the numeral 39 forms the remainingportion of the apparatus for continuous production of printed circuits.The basic structure for assembly 39 consists of two side pieces 47 and"48 separated by "and connected to a rectangular sheet 46 curvedateither end was to form anair tight inverted closure. Each of the sideplates 47 "and 48 is formed withtwo integral Vertically extendingprojections at either end. Alhole is drilled in each projection so thatthe viewed in Figures and 6 as shown by the end view in Figure 7, shaft57 is supported at one end by projection 49 of side plate 47 and at theother end by projection 53 of side plate 48. A pulley 58 is mounted onshaft 57 and fixed to rotate with the shaft by a key 59. A pulley 60 ismounted at the other end and fixed to rotate with shaft 57 by a key notshown. Shaft 57 extends beyond projection 53 and mounts a spur gear 61which serves as the drive connection for the assembly. Verticallydownward from shaft 57, projections 50 and 54 in side plates47 and 48respectively mount and support shaft 62. Pulleys 63 and 64 arepositioned at either end of shaft 62 with pulley 63 in verticalalignment with pulley 58 on shaft 57 and similarly, pulley 64 withpulley 60. Unlike the pulleys on shaft 57, pulleys 63 and 64 are free toturn on shaft 62. In a corresponding construction, the upper projections51 and 55 at the opposite end of side plates 47 and 48 respectivelymount and support shaft 74 which in turn mounts two freely rotatablepulleys 75 and 76. Lower projections 52 and 56 mount and support shaft71 with the two freely rotatable pulleys 72 and 73 mounted on shaft 71.

Each of the side plates carries two stub shafts located on a lineapproximately at the mid-point between the shafts carried by thevertically extending projections but offset at either end a requiredamount from a vertical line between the shafts. Side plate 48 carriesstub shafts 65a and 68a which mount pulleys 66 and 69 respectively. Sideplate 47 carries the stub shafts 65b and 68b and stub shaft 65b mountspulley 67, but the pulley mounted on stub shaft 68b is not shown in anyview. Although no shown, the side plates are sufliciently reinforced atthe stub shaft mounting points to carry any side thrusts or loadsimposed on the shafts.

It can be seen from the foregoing description that the stub shafts andthe identical sides of assembly 39 allow the use of two identicalcontinuous rubber belts 77 and 78 in the conveyor system. Belt 77 isplaced first around stub shaft pulleys 66 and 69 and is then broughtdownward and placed around pulleys 63 and 72 and finally upward andaround pulleys 58 and 75. Similarly, belt 78 is placed around stub shaftpulley 67 and the pulley not shown and then in succession around pulleys64 and 73 and pulleys 60 and 76. The conveyor system is completed byplacing a series of plate supports 79 in between the two belts 77 and78. For this purpose, the continuous belts are drilled withappropriately spaced holes to receive pins 82 and 83 extending from theend of each printed circuit support 79 as shown in Figure 8. Assembly 39is supported from the upper edge of container 40 by cleats 85 and 86fixed to side wall 47 and by cleat 87 shown and a similar cleat notshown fixed to side wall 48.

Container 40 is filled with the etching fluid to a level above thenozzles 18 as indicated by the dotted line 84. Assembly 39 is thenplaced in container 40 and supported by the cleats 85, 86, 87 and asimilar cleat not shown. The lower edge of the inverted closure formedby the rectangular plate 46 and the side plates 47 and 48 extends belowthe fluid level and, as referred to above, the inverted closure forms afluid trap to separate the particles of etching fluid contained in theair. The printed circuits 81 are then placed in the slots .80 extendingacross the width of the plate supports 79 which provide a convenient andsimple means for inserting and removing plates in the process ofcontinuous production. As spur gear 61 is driven by a motor at theproper speed, the pulleys 58 and 60 rotate the belts 77 and 78 withtheir attendant plate supports 79 and printed circuits 81 as a unitwhile the remainder of the conveyor system rotatably supports and guidesthe printed circuits past the "6 nozzles 18 and in a path' to assist intrapping the particles of etching fluid contained in the exhaust airstream.

It will be noted that in Figure 6 the printed circuits 81 are carried atan angle to the direction of the etching fluid stream as produced by thehigh velocity air through nozzles 18. When the printed circuits arecarried in a horizontal position a problem arises in connection with theuse of multiple nozzles for etching. This problem is due to the factthat a stream of fluid upon striking a flat surface perpendicular to thefluid stream spreads out in all directions, so, when the streams offluids from two or more nozzles meet, a point of zero velocity fluidmovement is reached and the rate of etching decreases sharply. Bytilting the plate at a slight angle to the horizontal, these points ofzero fluid velocity are eliminated and a fast rate of etch is provided.By means of the present invention, it is possible to etch a circuit 4inches by 5 inches in approximately 3 minutes with a single nozzle ascompared with a time of 10 to 15 minutes for equipment similar to thatof the invention. The etching time can be even further reduced by theuse of multiple nozzles in the invention to approximately 1 /2 minutes.

Although the method and apparatus of the present invention have beendescribed in specific embodiments, nevertheless various changes andmodifications obvious to one skilled in the art are within the spirit,contemplation and the scope of this invention.

What is claimed is:

1. Apparatus for continuously etching articles that comprises meansdefining a completely enclosed space over an etching fluid, means tocontinuously introduce a plurality of articles to be etched through afluid seal and to withdraw continuously the etched articles through afluid seal, and means for projecting said etching fluid in streams ofhigh velocity against said articles.

2. Apparatus for etching that comprises an open container adapted tohold etching fluid, a member cooperating with said container adapted todefine a completely enclosed space over fluid held in said container anda path for gas to escape from said enclosed space, said path leadingthrough fluid held'in said container, wherein particles of etching fluidcontained in said gas are removed, a nozzle mounted in said containerbelow the level of etching fluid when same is in said container, meansto supply gas under pressure to said nozzle whereby to produce a steadystream of high velocity fluid, and means to hold an article to be etchedwithin said enclosed space in a position to be acted upon by said fluidstream.

3. Apparatus for etching that comprises an open container adapted tohold etching fluid, a lid for said container adapted to cooperate withsaid container to form.

therewith a fluid seal wherein particles of etching fluid contained in agas are removed and to define a completely enclosed space over fluidheld in said container, a nozzle mounted in said container below thelevel of etching fluid when same is in said container, means to supplygas under pressure to said nozzle and means to hold an article to beetched within said enclosed space.

4. Apparatus as defined in claim 2 wherein a plurality of nozzles areprovided.

5. Apparatus for etching that comprises an open container adapted tohold etching fluid having a circular bottom, an outer wall, and an innerwall having a slot therein to allow gas to pass therethrough, a lid forsaid container having a circular top, an outer wall that depends betweenthe outer and inner walls of said container to a point below the levelof etching fluid when same is in said container, and an inner wall thatdepends within said inner wall of said container and a point above thelevel of etching fluid when same is in said container, said containerand lid being thus arranged to define a completely enclosed space overfluid held in said container and to establish a gas path from withinsaid enclosed space to outside that passes through a fluid seal formedby the from the ends of said container and cooperatingthere.

with to define a completely 'enclosed space over fluid held in saidcontainer, means to convey articles to be etched between said covermeans and-one end of' said container, through said fluid at said endof-said container,

into said enclosed spaceQthrough said fluid at the other end of saidcontainer and between saidcover means and said other end of saidcontainer, and means tocause said fluid to etch said articles Whilethey'are passing through said enclosed space.

7. Apparatus as dfinedin claim6 wherein said means to etch said articlesincludes a'nozzle located on said raised central portion and means areprovided to supply said nozzle with gas under pressure.

8. Apparatus as defined in claim 6 wherein said means to convey articlesincludes twobelts, and "article holding means are connected between saidbelts.

9. Apparatus as defined in claim 6 wherein said means to etch includes aplurality of nozzleslocated on said raised central portion, means areprovided to supply said nozzles with gas under pressure, and said meansto convey includes means to hold said articles at an angle as they arepassed through said enclosed space.

10. A method for continually etching articles that comprisessuccessively feeding articles to be etched adjacent a body of etchingfluid, leading a stream of compressed gas to a nozzle within said bodyof etchingfluid above which each said articles passes, and causing saidetching fluid to flow under the influence of said gas through saidnozzle in a steady stream of high velocity against each said article asit passes said nozzle above said body of etching fluid to etch same.

11. A' method for continually etching articles that comprisessuccessively feeding articles to be etched adjacent a body of etchingfluid, leading compressed gas to a plurality of nozzles Within said bodyof etching fluid above which each said article passes, and cause saidetching fluid to flow under the influence of said compressed gas throughsaid'nozzles in a plurality of steady streams of high velocity againsteach said article as it passes said plurality of nozzles above said bodyof etching fluid to etch same.

12. A method as defined in claim IO'Wherein said gas is subsequently ledthrough a liquid trap to purify same before exhausting.

13. A1nethod as defined in claim 11 wherein said articles to be etchedare fed at an angle relative to said body of etching fluid.

14. The method for etching an article that comprises positioningan'articleto be etched above a body of etching fluid, leading a streamof compressed gas to a nozzle within said body of etching fluid, andcausing said etching fluid to flow under the influence of saidcompressedgas through said nozzle in a steady stream of high velocityagainst said article to etch same.

15. The method defined in claim 14 wherein said compressed gas is led toa plurality of nozzles within said body of etching fluid.

16. The method as defined in claim 14 which includes the further step ofsubsequently leading said-gas through a liquid trap to purify samebefore exhausting.

References Cited in the file of this patent UNITED STATES PATENTS627,430 Levy June 20, 1899 1,908,487 Powers May 9, 1933 2,437,528 HodilMar. 9, 1948 2,446,443 Tibbetts Aug. 3, 1948 2,568,803 Guenst Sept. 25,1951 FOREIGN PATENTS 167,298 Great Britain Aug. 8, 1921 U. S. DEPARTMENTOF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 2,825,167Conrad Skladal, Jr. March 4, l9i8 It is hereby certified that errorappears .in the printed specificat'xo of the above numbered patentrequiring correction and that the said Letter Patent should read ascorrected below.

Column 1, line 43, for "tube" read tub column 4, line 8, for "areas"read area column 6, line 70, for "and a" read and to a column '7, line36, for "articles" read article Signed and sealed this 17th day of June1958.

( A Attest:

KARL Ho APQINE ROBERT C. WATSO Attestlng cer Comnissioner of Patert

